Liquid crystal based devices are ubiquitous, enjoying applications ranging from miniaturized displays on portable phones, computers, and other devices, and small and large size monitors. Liquid crystal technology is also attractive for application in switchable windows.
In manufacturing LC cells, particularly large size LC cells, the step of LC filling is often a bottleneck. The main drawbacks of conventional processes such as “vacuum filling” and “vacuum pulling” include extensive processing time, as well as streaky appearance after curing (particularly along the LC filling holes). Thus, overall yield is low with conventional LC filling processes.
Similarly, in LCD manufacturing process, LC filling is a very slow and costly step. This is extremely important when panel sizes increase beyond, e.g., 20 inches (diagonal), with a very small (e.g., about 2 to 5 micrometers) cell gap. It is not uncomfortable for filling times to exceed 9 hours.
Conventional LC cell filling methods are based on creation of a pressure difference between the interior and exterior of an empty cell. Empty cells are generally pre-fabricated and placed inside of a vacuum chamber to create pressure difference. LC material is pushed into the cell through a filling hole when the pressure inside the chamber is resumed to 1 atmosphere. Evacuation of air from the interior of the empty LC cell is an extremely slow process, especially when the size of the LC panels increases in dimensions.
Though a “one-drop” filling method has been developed in recent years that has reduced filling time from hours to minutes, many of the steps (LC dispensing, sealant dispensing and curing, cell registration) must be carried out in a vacuum environment in order to avoid trapping air bubbles. Such process requires sophisticated systems, requiring high equipment cost and inconvenient operation.
The conventional one-drop-filling methods attempted to reduce the time of LC cell filling by dispensing the LC materials in a controllable manner within a vacuum environment. Trapped vacuum bubbles are compressed and eliminated after the cell is brought to 1 atmosphere. However, the one-drop-filling method is not a suitable solution for atmospheric environments, due to the fact that its dispensing mechanism will result in trapped bubbles. Therefore the process is still complicated and costly with the requirement of a vacuum environment for steps such as dispensing, registration, and lamination.
Therefore, a need remains in the art of LC cell fabrication for an LC dispensing mechanism capable of operation (partially or in its entirety) in pressure conditions other than vacuum conditions, or other than systems requiring substantial pressure differential as is required for conventional LC filling systems and methods. Such systems must minimize or eliminate formation of bubbles in the resulting LC panels.